The invention relates to a transducer for a path tracer with several normally opened switches arranged in a row along a path to be measured. The switches can be closed by a switching magnet, without contact therewith for a time during which the switching magnet faces each switch, while being moved along the row of switches. The switching magnet or the element to which the magnet is fastened is moved relative to the row of switches. It is insignificant in this connection, if the switching magnet is moved along the stationary row of switches or vice versa. With a known transducer of the type described, the switching magnet is moved along the row of switches by means of a float. The switches are arranged at such a spacing, that in any case only one switch can be closed. Each switch is associated with a flip-flop circuit, which circuit is closed by means of its associated switch and is opened again when the following switch is closed, so that always one flip-flop circuit is switched on. An indication is provided, of which flip-flop circuit is switched on, thus giving a stepwise indication of the level of the float. It is an object of the invention to improve the accuracy of measurement by simple means, and such object is achieved, by providing that at any position of the switching magnet facing the row of switches at least one switch is closed and that the switches are individually led away from a common measuring line and are connected sequentially to taps of a row of taps of a series circuit of resistors. The values of the resistances between the taps are converted by electric means into an output of measured values. The accuracy of measurement with such transducers is improved as the spacings between the switches in the row of switches are made smaller. According to the invention, such spacings can be very much smaller than with known transducer, because the only condition which must be ensured for a proper functioning is that in all cases at least one switch must be closed, and the functioning of the device will not be disturbed if in addition, for example due to magnetic dispersion, some other switches are also closed. Each switch needs only a section of the resistance of the series circuit of resistors with a respective tap, so that the circuitry is maintained simple, even if many switches are provided. In the most simple case, the output of the measured value is the electrical indication of the measured value of the resistance, which can be obtained in a simple manner and by means of potentiometers with three lines. Under certain circumstances, a simple measurement of resistors with only two lines, which can be tapped from the series circuit of resistors, will be possible. The electrical connection between the measuring point and the indicating point consequently requires only a small amount of line wire and a DC source will suffice for its operation. The invention has a versatile application, so that the measured path may be a straight line, curved or cornered, for example a segment of a circular arc, a full circle interrupted by the series circuit of resistors inserted at any point along the circumference, a path along the corners of a right-angled triangle, or a three-dimensional curvature, for example a helix. According to the invention, a closed switch must not open after the switching magnet has passed it and until the following switch is closed. Otherwise, the continuous alteration of the tapped resistor value would be interrupted. In case the switching magnet travels along, the row of switches in both directions, as in most applications, the accuracy of measuring will be higher the lower the amount of switches which can be closed simultaneously by the magnet. In the interest of a high accuracy, a further construction of the invention provides that the switching magnet will simultaneously effect the closing of both switches, when facing the space between two switches, but will not effect any other switch located at a larger distance.
In the interest of a higher accuracy of measurement, it is desirable, that the magnetic efficiency of the switching magnet be concentrated in a beam and especially suitable for this purpose is a ring put mounted around row of switches, which ring is magnetized permanently with its magnetic flux running in the radial direction.
The measured path can be easily indicated in linear terms by means of the invention. It is recommended for this purpose that the resistance value between two adjacent taps must be of equal size and that switches of the same type be arranged in rows at equal intervals. In such case, the tapped value of resistance is proportional to the measured path and in the case that the value of resistance is indicated in linear terms, then also the indication of the measured value would be linear. If, however, a non-linear indication is required, this can be easily done by a proper dimensioning in relation to the required functional dependency of the output of the measured value, either the interspacing of the switches, or the spacings between the switches, of the series resistor circuit or both values. The row of switches required according to the invention, with the associated series circuit of resistors, can be easily built as a standardized component which can be produced in defined lengths and if intermediate dimensions are required, they may be shortened to the required length. For such standardized circuit components, always the same indicating instrument can be used and a single setting resistor will suffice for adjusting the differing lengths of the resistors of the circuit.
A preferred construction of a standardized circuit element as described is characterized in that the switches, each of which is melted into a respective glass tube arranged on one flat side of an insulated flat carrier strip and having connecting line wires led out opposite ends, are arranged at an acute angle to the path to be measured and along the longitudinal axes of the glass tubes. The switches are arranged along the direction of the path to be measured in an overlapping manner. Connections located on the other side of the carrier strip are connected to the series circuit of resistors. The measuring line and the series circuit of resistors are arranged on the other flat side of the flat carrier strip.
The invention is preferably employed for indicating the level of liquids in containers. A suitable construction is characterized in that the switching magnet is arranged on a float body and that the magnet and float body slide along a guide tube, in the interior of which the carrier strip equipped with the switches and series resistor circuit is housed, thus protected against the access of liquid.
The invention is not limited to this application. It can be used for example for the measurement of paths, in which an element possibly equipped with a permanent magnet is moved along a limited path of measurement within the limits of the switching speed of the switches, for example for measuring the floating position of a floating body which is situated in a floating liquid, and for indicating the angular position of the rudder of a ship.
These and further objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show for purposes of illustration only several embodiments in accordance with the present invention.